1. Field of the Invention
The present invention relates to machinery for forming box blanks from corrugated paperboard sheet material.
2. Description of the Prior Art
Corrugated paperboard box blanks are fabricated from uniform corrugated sheet material by the selective placement of scores, slots and slits in a blank sheet. Such scores, slots and slits are applied by rotary dies or knives as individual sheet units are nip driven along a machine path between respective die or knife sets.
At commercial production rates and speeds, this material forming process represents severe service for the production machinery due to the strength, stiffness and abrasiveness of the process material. One consequence of such service severity is a tendency of the mating die and knife sets to laterally misalign under the operational stress. Cutting and scoring edges destructively clash together.
To reduce and control such damaging misalignment, these rotary units have been laterally stabilized with a rotational thrust bearing mechanism characterized as a "yoke" and "head" set. Each rotary die, knife or scoring wheel is integrally paired with a massive annular groove wheel called a "head." A cooperative "yoke" includes two finger projections from an integral heel section that is secured to the machine frame. Tips of the finger projections mesh with the head groove space on diametrically opposite sides of the wheel unit. Bushing pads or bearings secured to the stationary yoke tips slide in contact with the rotating head groove walls. Lateral stress on the die, knife or scoring wheel is directly transferred to and resisted by the yoke fingers. Simultaneously, however, wear loss of the finger bushing pad material increasingly reduces the sliding contact bias against the head groove walls. After sufficient wear, the bushing pads must be either replaced or repaired. Repair constitutes the insertion of a shim between the bushing pad and the finger structure. In either case, repair or replacement, correction is time consuming and expensive due to the consequential loss of production time.
In recognition of this maintenance burden against corrugated box making machinery, the Gartech Manufacturing Co. of Litchfield, Il. has introduced a stabilizer assembly design which includes two roller bearings mounted within each yoke finger in lieu of traditional bushing pads. These two roller bearings are transversely positioned across the finger thickness whereby each outer race surface runs against a respective head groove wall.
Although the Gartech stabilizer assembly design is an effective solution to the maintenance burdens created by yoke trust pad wear, the design is sufficiently expensive to manufacture as to largely negate the maintenance savings from the design.
It is, therefore, an objective of the present invention to provide a corrugated box machine rotational stabilizer assembly that is both inexpensive to manufacture and requires no machine down time to adjust.
Another object of the present invention is to provide an adjustable thrust bushing mechanism for corrugated box machine rotational stabilizers that will fit within the dimensional confines of traditional head grooves and yoke fingers.
Another object of the present invention is to provide an adjustable thrust bushing mechanism for corrugated box machine rotational stabilizers that may be adjusted for wear without interrupting the machine operation.